evaluation of time-area accuracy in developing iuh

the hydrograph at watershed outlet can be expressed as hydrological response of watershed to geomorphological behavior. in present study with the aid of the gis and the concept of instantaneous unit hydrograph, the watershed response was simulated. in present physical method, the iuh is derived from three parameters of time of concentration, storage coefficient and time-area curve of the basin. in the present study, the accuracy of various methods of determining time-area curve in providing clark instantaneous unit hydrograph viz. channel profile, average velocity and laurenson methods were therefore evaluated. the comparison of estimated and observed hydrographs by using qualitative and quantitative criteria showed that the average velocity method has had the highest accuracy in estimation of time-area method. the results of the quantitative statistics of root mean square of error, bias in peak discharge, coefficient of efficiency, and relative errors in peak discharge, time to peak and base time were respectively found to be 1.39, 0.93, 0.83, and 7.13, 33.33 and 15.38%. the results of this research also showed that the clark model had a good efficiency in simulation of unit hydrograph in kasilian watershed, mazandaran province, iran.